Found today at the Intertoys store in downtown Herne. They had two sets.

Fellow German fan Metro, a member of the Starblight.de community, also found the set at the Intertoys store inside the Shopping Arkaden shopping mall in downtown Bocholt last week.

Some disclaimers:
1) Intertoys is a mostly regional chain with a Dutch parent company. Most of their stores are located in the federal state of North Rhine-Westphalia, near the Dutch border.
2) As a consequence of the above, Intertoys supposedly gets its stock of Hasbro toys through the Hasbro Netherlands supply chain, which has in the past occasionally resulted in German Intertoys stores stocking toys that were either never officially supposed to be available at German retail (e.g. Energon combiners, or Cybertron toys in 2005), or were officially supposed to be exclusive to another chain in Germany (e.g. AOE Deluxes and Voyagers at Toys"R"Us).
3) On top of that, the stores in Bocholt and downtown Herne, where this set was spotted, both have occasionally been given "special treatment" in the past, insofar as I've found some toys (both Transformers and Nerf products) at each store that I've never seen at any other German Intertoys store. The store in downtown Herne is effectively their "flagship store" for Germany, located in the same building as the German Intertoys corporate headquarters, while the city of Bocholt is directly bordering the Dutch border. So it could very well be that the Mini-Con 4-Pack will never see a wide release at German Intertoys stores.

Hasbro is being really odd again - these have been out in Hungary for half a year or so. I wish the other 4-pack with Hammer and Anvil would be released!
Never understood their "logic", you'd think Germany is considered a bigger market for toys than Hungary...